In general, polyimide resins have high heat resistance and good electrical insulation, and find use in printed circuit boards and heat resistant adhesive tapes. They are also used as resin varnish to form surface protective films and interlayer insulating films for electric parts and semiconductor materials. Polyimide resins, however, are soluble only in a limited number of solvents. Accordingly, it is a common practice to coat the substrate with a solution of polyamic acid which is a precursor for polyimide and relatively soluble in various-solvents, and then to treat the coating at an elevated temperature to effect dehydration and cyclization into a polyimide resin.
Meanwhile, for the purpose of improving the solubility of polyimide resins in solvents, enhancing the adhesion thereof to substrates, and imparting flexibility thereto, an attempt has been made to introduce siloxane chains into polyimide skeletons. However also in these cases, the polyimide resin has to be generally diluted with solvent for use. This necessitates a step to remove the solvent, such as a heating step, after the polyimide resin solution is applied or coated to substrates. Further, measures for working environment, such as ventilation, are also required.